ICF-Like protease (caspase) is involved in transforming growth factor β1-mediated apoptosis in FaO rat hepatoma cell line

Transforming growth factor-beta(1) (TGF-beta(1)) arrests growth and/or stimulates apoptosis of a variety of cells. The biochemical pathways involved in the apoptotic processes, however, remain poorly defined. TGF-beta(1) induces DNA fragmentation together with morphological changes, which are characteristic of apoptosis in the FaO rat hepatoma cell line. Histones were remarkably enriched in lysates of these cells during TGF beta(1)-induced apoptosis. We identified U1-70 kd as a death substrate which is cleaved following TGF-beta(1) treatment. The tetrapeptide caspase inhibitor carbobenzoxy-valyl-alanly-aspartyl-(beta-O-methyl)-fluoromethyl ketone (ZVAD-FMK) prevented TGF beta(1)-induced apoptotic DNA fragmentation and cleavage of the U1-70 kd protein, showing that caspase(s) are involved in TGF beta(1)-mediated apoptosis. To identify specific caspases involved in apoptosis induced by TGF-beta(1) in FaO cells, proteolytic activation of several of these caspases and their substrates were studied as a function of time following TGF beta(1)-treatment. TGF beta(1)-treatment induced the progressive proteolytic processing of caspase-2 (ICH-1L/Nedd-2), whereas caspase-1 itself did not show any cleavage from the precursor. Pretreatment with ZVAD-FMK abrogated the maturation of caspase-2 and blocked the apoptotic progress. These results suggest that caspase-2, but not caspase-1, may play a crucial role in TGF beta(1)-induced apoptosis in these cells.